The present invention relates generally to methods and devices for delivering and deploying a medical endoprosthesis, and more particularly to a delivery system for a self-expanding endoprosthesis.
Medical endoprostheses, commonly referred to as stents, are known in the prior art for maintaining the patency of a diseased or weakened vessel or other passageway. Stents have been implanted in various body passageways such as blood vessels, the urinary tract, the biliary tract, and other body lumens. These devices are inserted into the vessel, positioned across the treatment area and then expanded or allowed to self expand to keep the vessel or passageway open. Effectively, the stent overcomes the natural tendency of the weakened area to close. Stents used in the vascular system are generally implanted transluminally during or following percutaneous transluminal angioplasty.
Self expanding stents may be mechanically compressed springs which expand when released, and/or they may be constructed from shape-memory materials including shape memory polymers and metals such a nickel-titanium (Nitinol) alloys and the like which have shape-memory characteristics.
Delivery devices for self expanding stents have included a protective sheath to prevent premature expansion at body temperatures for heat induced shape memory devices or to contain mechanically restrained or stress induced shape memory devices. The sheath also enhances the delivery through the tortuous vessels of the vascular system. Such sheaths increase the profile of the delivery system, necessitating use of a delivery catheter with a large diameter. The large diameter of the delivery catheter may in turn increase the risk of complications at the patient access site.
The increased profile also detracts from the ability of the device to navigate through tortuous vessels or passageways. The increased cross-sectional profile of the delivery system may make it impossible to deliver a self expanding stent to the treatment area and may decrease the ability to deliver sufficient contrast material through the guide catheter for enabling precise positioning.
In addition to the large profile of the delivery system, another problem associated with self expanding stents is that the stent itself cannot be radially compressed to a low profile. Since most such stents are cut from a tubular member, they are limited to the radial size of the tube from which they were cut. As explained above, it is desirable to keep the profile of the stent as small as possible. Furthermore, deploying a self expanding stent requires manipulating the outer sheath while keeping the stent carrying shaft stationary in order to properly place the stent at the treatment site.
In the event that a distal protection device is being used during the vascular procedure, the present invention can be used for retrieving the distal protection device. Distal protection devices are delivered via a guidewire and are positioned distal of the treatment area where they are expanded across the vessel to capture emboli that may escape during the procedure or placement of the stent. These devices are often self expanding and thus deployed and retrieved with a sheath. The procedure can become very time consuming if the delivery system must be completely removed after the procedure and then the distal protection device sheath be reinserted to withdraw the catheter. Thus, it would be an advantage to use the delivery device as the retrieval device for the distal protection device.
Therefore, what is needed is a delivery system that addresses the problem of compressing the self expanding stent to a lower profile than that achieved with conventional stent delivery systems. A stent delivery system that is easy to manipulate, has a low profile and can also accommodate a distal protection device is also needed.
The present invention is a delivery system for a self expanding stent that has in catheter with an outer shaft moveable with respect to an inner shaft for releasing a stent. The stent is positioned on the inner shaft and restrained by the outer shaft until it is released at the treatment site. The catheter tip is mounted on the inner shaft and is tapered to provide a smooth transition from the catheter outer shaft to the guidewire extending distally of the delivery system. A handle is located on the proximal end for one-handed operation when deploying the stent.
The system may include a valve relief that is selectively coupled to the catheter. By coupling the valve relief to the hemostatic valve or tuohy-borst coupler, the catheter can be moved within the hemostatic valve while reducing back bleed.
The catheter may deploy a stent retained in one of two configurations. In the first configuration, all the stent segments are compressed together and have the same radial position about the inner shaft. In the second configuration, certain stent segments are positioned within the other stent segments such that some have a first radial position and some have a second radial position. The second position is achieved by pressing certain segments inward after the first stent roll down to the first position when all the segments have the same radial position.
In alternative embodiments of the delivery system, the catheter outer shaft may extend past the inner shaft. This creates an area within the delivery system for retrieving a distal protection device. Alternatively, the inner shaft can be withdrawn sufficiently within the outer shaft to create an area to accommodate a distal protection device for retrieval with the delivery system catheter.